Preheat oven to 350°F. Sift the first three ingredients together and set them aside. Beat the eggs in a mixing bowl until light and lemon-colored. Add the vanilla extract. Gradually beat in the sugar. Continue beating, on high speed, until the volume has increased to four times the original amount, about 8 minutes. Gradually fold in the flour mixture and the lemon rind. Stir in the 3/4 cup of melted butter.

Brush madeleine pan generously with additional melted butter. Spoon one slightly heaping tablespoon of batter into each shell, filling them 2/3 full. Bake 10 to 12 minutes or until a toothpick inserted in the center comes out clean. Remove the cakes from the pan by gently lifting the edge with a fork. Cool on racks covered with parchment paper. Sift confectioner's sugar over the tops.